Add complex UI docs and samples

samples/rich-gui-basic-sample.lua

@@ -0,0 +1,16 @@
+-- name = "Rich GUI Basic sample"
+
+function on_resume()
+    my_gui = gui{
+        {"text", "First line"},
+        {"new_line", 1},
+        {"text", "Second line"},
+        {"new_line", 2},
+        {"button", "Button #1"},
+        {"spacer", 2},
+        {"button", "Button #2"},
+    }
+
+    my_gui.render()
+end
+